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Title: A live-attenuated chimeric PCV2 vaccine based on subtype 2b is transmitted to contact pigs but is not upregulated by concurrent infection with PPV and PRRSV and is efficacious in a triple challenge co-infection model

Interpretive Summary: Porcine circovirus associated disease (PCVAD) is a syndrome that affects many young pigs and can be caused by a variety of factors. The predominant factor is porcine circovirus type 2 (PCV2), a swine virus that was discovered in North America in the mid 1990s. Soon after the discovery of PCV2, a similar virus was identified in Europe leading to the sub-typing of PCV2 into a North American lineage - PCV2a, and a European lineage - PCV2b. In 2005, epidemics of PCVAD were occurring in North America and diagnostic investigations identified PCV2b in North America for the first time. PCV2 vaccines that were derived from the PCV2a lineage became commercially available in 2006. The vaccines are all inactivated vaccines and have worked well, even reducing losses that are attributed to the PCV2b lineage. However, there are times where there is a question about the efficacy of the vaccines. As part of ongoing research projects to evaluate new PCV2 vaccine concepts, an experimental modified-live PCV2 vaccine was made with PCV2b components to test in pigs. This report describes experimental studies in young pigs demonstrating the next generation vaccine was protective against PCV2b challenge, was safe to use, and has potential to be administered with drinking water.

Technical Abstract: The objective of this study was to determine the safety and efficacy of a new live-attenuated chimeric PCV1/2b vaccine. Forty-six, 21-day-old, PCV2-naïve pigs were randomly assigned to one of six groups (Negative controls, positive controls, Vac-0, Vac-0-PCV2, Contact-PCV2, Vac-28-PCV2). All pigs were challenged with PCV2b, PRRSV and PPV. One of eight positive control pigs developed clinical signs and 3/9 Vac-28-PCV2 pigs developed severe PCV2-associated microscopic lesions. Vac-0-PCV2 pigs had significantly (p<0.05) decreased amounts of PCV2 DNA in tissues and sera, and significantly (p<0.05) reduced microscopic and macroscopic lesions. PCV1-2b vaccine virus DNA levels remained similar in all vaccinated pigs. Contact-PCV2 pigs became PCV1-2b viremic and were protected against PCV2b challenge.